This invention relates to a novel developer adapted to electrophotography, electrostatic recording, magnetic recording, etc., and an image forming method using the same.
In electrophotography, an electrostatic latent image is first formed through utilization of the photoconductors such as cadmium sulfide, polyvinylcarbazole, selenium, zinc oxide, etc., for example, by uniformly imparting charges on a photoconductor layer, and by applying an imagewise exposure to the photoconductor. The electrostatic latent image is developed with a powdery toner or developer charged to the opposite polarity to that of the electrostatic latent image and, if desired, the developed image is further transferred to a transfer sheet, followed by fixing.
Of these processes, especially in the case of a device having the transfer step, it is generally practiced to remove the residual toner on the photosensitive member not transferred and use the photosensitive member repeatedly.
For removing the residual toner on the photosensitive member, a cleaning member is generally brought into contact with the photosensitive member as practiced in the blade cleaning system, the fur brush cleaning system or the magnetic brush cleaning system. In this case, the cleaning member contacts the photosensitive member under an appropraite pressure, and therefore the photoconductive member may be damaged or the toner may stick onto the photosensitive member. In order to avoid sticking of the toner onto the photosensitive member, it has been proposed to add both a waxy friction-reducing material and an abrasive material into the toner, as disclosed in Japanese Laid-Open Patent Application No. 47345/1973. This method is indeed effective for avoiding sticking of toner, but involves the following drawback. That is, when a friction-reducing material is added in an amount enough to avoid toner sticking, it will become difficult to remove materials with low electric resistance such as paper powder, ozone-oxidation product, etc. formed on or sticking onto the surface of the photosensitive member after repeated uses. In particular, in an environment of high temperature and high humidity, a defect is observed that the latent image on the photosensitive member is damaged by the materials with low electric resistance.
Also, it is difficult to control the amounts of the friction-reducing material and the abrasive material to be added, and therefore difficult to obtain a developer having stable characteristics. If the abrasive material is added in an amount sufficient to remove the sticking onto the photosensitive member, some troubles may be caused, such as damaging of the photosensitive member or damaging of the cleaning blade, whereby cleaning cannot satisfactorily be performed.